1. Field of the Invention
This invention relates to an exhaust gas purification system of internal combustion engines.
2. Description of the Related Art
Internal combustion engines are ordinarily provided with a catalytic converter comprising a three-way catalyst in the exhaust system which removes HC, NOx and CO components in the exhaust gas generated by the engine. However, when the catalytic converter is not activated, for example, at the time of engine cold-starting, unburned components of the exhaust gas including unburned HC are released immediately into the atmosphere.
For that reason, as taught by Japanese Laid-Open Patent Application No. Hei 10 (1998)-153112, there has been proposed an exhaust gas purification system which has an adsorbent made of a zeolite material or some similar material installed in a bypass exhaust gas passage branched from the exhaust pipe at a location downstream of the catalytic converter, which again merges into the exhaust pipe at a downstream point, and a switch-over valve to be controlled to open or close the bypass exhaust gas passage. The switch-over valve is controlled to open the bypass exhaust gas passage when the catalytic converter has not been activated at cold engine start to introduce the exhaust gas such that the adsorbent adsorbs unburned components and to close the bypass exhaust gas passage such that the adsorbed components desorb from the adsorbed components.
The desorbed components are thereafter recirculated at a position upstream of the catalytic converter, e.g. to the air intake system, through an EGR passage after the catalytic converter has been activated. It is also known to provide an ordinary catalytic converter at the bypass exhaust gas passage to improve catalytic purification efficiency, as is disclosed in Japanese Laid-Open Patent Application No. Sho 50-20129.
As is disclosed in Japanese Laid-Open Patent Application No. 2001-200720, such an EGR passage is constituted as a pipe which extends from the air intake system to the bypass exhaust gas passage. The structure of the EGR passage disclosed in this prior art (""720) requires another pipe for forming an inlet which is to be penetrated through a case (constituting the bypass exhaust gas passage) and joined to there. This increases steps of fabrication and cost. Further, the possibility of leakage increases as the number of joints increases.
Moreover, this configuration makes it difficult to remove the exhaust gas purification system from the branch pipe (and the upstream exhaust pipe coupled to the branch pipe through flange, and is disadvantageous in maintenance.
Aside from the above, in such a kind of exhaust gas purification system, as is disclosed in the aforesaid prior art reference (""112), the exhaust pipe (constituting a main exhaust gas passage) and the case (constituting the bypass exhaust gas passage) are joined and fixed together at both ends in upstream and downstream locations (in the sense of exhaust gas stream). Since, however, the exhaust gas is regulated to flow one of the exhaust pipe and the chamber alternatively, it is preferable to avoid deformation or distortion due to thermal stress which could occur when the pipe and the chamber are different in temperature.
A first object of the invention is therefore to provide an exhaust gas purification system of internal combustion engines having a recirculation pipe that recirculates unburned exhaust gas components desorbed from an adsorbent installed in a bypass exhaust gas passage to a location upstream of the catalytic converter, which is configured to have a simplified structure of the recirculation pipe inlet for the bypass exhaust gas passage.
A second object of the invention is therefore to provide an exhaust gas purification system of internal combustion engines having a main exhaust gas passage and a bypass exhaust gas passage storing an exhaust gas purifier, which is configured to avoid deformation or distortion due to thermal stress which could occur when the passages are different in temperature.
In order to achieve the first object, the present invention provides a system for purifying exhaust gas of an internal combustion engine having an exhaust pipe for discharging exhaust gas generated by the engine to exterior of the engine through a catalytic converter, a branch pipe coupled to the exhaust pipe through a flange at a location downstream of the catalytic converter and having a main exhaust gas passage and a bypass exhaust gas passage, a switch-over valve for selectively connecting the exhaust pipe to the main exhaust gas passage or the bypass exhaust gas passage, an adsorbent installed in the bypass exhaust gas passage for adsorbing unburned components of the exhaust gas, and a recirculation pipe for recirculates the exhaust gas including the unburned components at a location upstream of the catalytic converter; wherein the improvement comprises; an inlet of the recirculation pipe for introducing the recirculated gas is formed integrally with the branch pipe flange.
In order to achieve the second object, the present invention provides a system for purifying exhaust gas of an internal combustion engine having a bypass exhaust gas passage storing an exhaust gas purifier, the bypass exhaust gas passage branching from an exhaust pipe for discharging the exhaust gas generated by the engine and merging into the exhaust pipe at a location downstream of the exhaust gas purifier through a main exhaust gas passage connecting to the exhaust pipe, comprising; a first case constituting the bypass exhaust gas passage; and a second case constituting the main exhaust gas passage; wherein: the first case and the second case are configured in such a way that one is displaceable relative to other.